A trailer coupling for a tractor/trailer combination as a rule comprises a coupling lock with a receptacle in which a coupling element can be inserted. The coupling lock and the coupling element form an articulated joint so that the tractor vehicle can pivot relative to the trailer vehicle, for example when the combination has to drive round a curve. In this case the coupling lock is fixed on one vehicle of the combination and the coupling element on the other vehicle thereof. If the tractor vehicle is a passenger automobile, then as a rule the coupling element is attached to the tractor vehicle and comprises a ball head, which engages in the receptacle of the coupling lock in the form of a ball socket, fixed on the towbar of the trailer vehicle. Until now no system that is sufficiently well developed for mass production has been available for sensing the pivot angle between the coupling element and the coupling lock, which is also referred to as the combination angle. In attempts to stabilize the combination, the combination angle is determined, for example, with an arrangement of cable potentiometers. These or other length measurement sensors (ultrasonic, laser, radar) measure the distance between the rear bumper of the tractor vehicle and a suitable front surface of the trailer vehicle. The distance is off-center relative to the vehicle and varies as a function of the combination angle. The translation length variation of the distance is converted by a computer into a rotational angle signal. The disadvantage of this is that owing to measuring equipment of this type the coupling and decoupling of the trailer vehicle is no longer possible, or much more difficult, since the measuring equipment comprises part-systems on both the tractor vehicle and the trailer, which are sometimes even connected together mechanically. Moreover, such measuring equipment is as a rule not suitable for operation under adverse environmental conditions (humidity, temperatures).